The physical properties of methane change drastically and the phenomenon of phase change vanishes under supercritical pressure, so the heat exchange process is extremely complex. The heat transfer characteristics of supercritical methane in a heating vertical circular tube were investigated numerically. The thermal performance and transport properties of supercritical methane were obtained by introducing the material model of methane in the refrigerant properties software REFPROP. The results show that it is advantageous to the heat transfer when the averaged fluid temperature is close to the critical temperature and the wall temperature is higher than the critical temperature. And the heat transfer coefficient increases with the decrease of pressure. High heat flux and low mass flow rate will cause the deterioration of heat transfer. Then the influence of buoyancy on the heat transfer was studied carefully and the buoyancy judgment standard suitable for methane was obtained. It is found that the buoyancy which changes the distribution of radial velocity and inhibits the generation of turbulent kinetic energy weakens the convective heat transfer.